This invention relates to electronic timepieces, and more particularly to an electronic chronograph watch of the type provided with a quartz time standard, a watch motor actuating step-wise a time-period counting device comprising a central seconds-counter, and a push-button control mechanism for starting, stopping, and resetting the counting device, this mechanism controlling a pulse counter connected to the time standard, the input signal of which pulse counter is at a frequency higher than 1 c/s, and the output signal of which pulse counter controls the chronograph motor at a frequency lower that 10 c/s.
Mechanically driven chronograph watches generally comprise a sweep seconds-hand which, when the chronograph is running, is coupled to the wheel train and consequently advances step by step at the frequency given by the hair-spring-balance system, i.e., usually at a frequency of 18,000 vibrations per hour. When this hand moves over a dial on the order of 25-30 mm. in diameter, the step-by-step movement of its tip along the hour-circle is easy to read, so that a period of time measured by the chronograph device can be read with an accuracy of one-fifth of a second by means of this hand. When the hairspring-balance system has a frequency of 36,000 vibrations per hour, a measured period of time can even be read with an accuracy of one-tenth of a second by means of the chronograph seconds-hand.
Attempts have already been made to produce electronic-type chronograph watches, but until now no satisfactory solution has been thought of as concerns a sensible presentation of the data counted and displayed by the chronograph mechanism.
U.S. Pat. No. 3,884,035 teaches that in designing an electronic chronograph watch having a quartz time standard with a frequency divider which supplies signals at a frequency suitable for driving a stepping motor actuating a time-display wheel train, it is advisable to provide an intermediate output in the frequency divider in order to have an intermediate signal at a frequency which is at least on the order of 10 c/s and to divide this intermediate signal separately into a frequency, conveniently 1 c/s, to actuate a stepping motor driving a display mechanism comprising a chronograph seconds-hand and, as the case may be, a minute-counter and an hour-counter. As a matter of fact, the use of a stepping motor actuated at a frequency of 1 c/s is compatible with the service life of batteries suitable for being accommodated in the case of a chronograph watch intended to be worn as a wrist watch, and two motors of this kind can be driven by a power source of appropriate capacity. With such a design, however, the periods of time measured by the chronograph device cannot be ascertained with greater accuracy than one second.
To remedy this drawback, the above-mentioned U.S. patent likewise provides for an intermediate output from the auxiliary frequency divider and the driving of a third motor at a frequency which may be higher than 1 c/s.
In this case, the display device of the chronograph will include a seconds-hand jumping step-wise at the rhythm of 1 c/s, plus a hand indicating fractions of a second. However, the complexity of such a system is a serious obstacle to its commercial production.
The chronograph watch described in U.K. Published Application No. 2,028,545, on the other hand, uses only two stepping motors, one actuating the wheel train indicating the time of day, the other actuating the chronograph train. In this case, in order that periods of time may be read with greater accuracy than one second, the chronograph motor is driven by pulses which leave the counting circuit at a frequency of 10 c/s. On the other hand, the sweep seconds-hand forming part of the chronograph display mechanism is driven at a speed of rotation ten times the normal speed, so that it accomplishes one revolution over the dial in six seconds. It is thus possible to read tenths of a second, but the reduction ratios which must be provided for in the chronograph train for driving a minute-counter and an hour-counter are then such that the chronograph watch movement becomes excessively bulky. On the other hand, periods of less than one minute but more than six seconds are much less easy to read than with a conventional display.
More recently (see U.K. Published Application No. 2,067,798), another solution has been proposed to remedy the difficulties thus encountered: the chronograph motor is driven at a frequency of 1 c/s and actuates a sweep seconds-hand which jumps through an angle of 6 degrees at each step of the motor, while the motor driving the device displaying the time of day is driven normally at a frequency of one-sixth c/s, or one step every six seconds, and actuates a small offset seconds-hand effecting one revolution per minute at the rate of ten jumps per minute. Moreover, the intermediate counter which controls the chronograph motor is associated with a memory and connected to the time-of-day display motor, so that when the chronograph motor is blocked after a period of time has been measured, the contents of the intermediate counter are compared with the position of the small seconds-hand, and the time-of-day display motor receives a number of pulse such that the position of the small seconds-hand indicates the tenths of seconds of the period of time which has just been measured.
This solution solves the difficulties of bulkiness and of supplying power to the control circuit of the chronograph watch, but it remains complicated to read the period of time measured. In addition, if a reading has to be made at a glance, i.e., just as the counters are being reset so that counting can continue immediately, this solution excludes the possibility of reading fractions of a second.
It is therefore an object of this invention to provide a chronograph watch in which the various functions desired are presented and displayed under the most sensible possible conditions in order to enable clear, easy, and accurate reading of the data supplied.
A further object of this invention is to remedy the drawbacks described above by providing an electronic-type chronograph watch wherein the chronograph device comprises a sweep seconds-hand, and the fractions of a second can be displayed and read easily and accurately.
To this end, in the electronic chronograph watch according to the present invention, of the type initially mentioned, the counter further transmits at least one intermediate signal at a frequency intermediate between those of the input and output signals, and the intermediate signal or signals control an electro-optical display device indicating the fractions of a second while the chronograph is running.